Twelve-lobe fastener



P 10, 1963 e. w. senses: 3,400,626

7 TYELVE-LOBE FASTENBR I Filed llarch 13. 1967 FIG. I

GIVEN D u .FIG.5

v INVENTOR: EMRIC W. BERC-iERE United States Patent 1 Claim. (Cl. 85-9)ABSTRACT OF THE DISCLOSURE Fastening devices either in the form ofthreaded bolts or threaded nuts having a specialized exterior wrenchingcontour for engagement by the recesses of a standard double hexagonwrenching tool socket of mating size. The wrenching contour of thefastener is such that the standard wrenching tool sockets can be usedand yet a considerably higher torque can be applied before failure ofthe socket. The actual wrenching contour is defined by twelve lobescircumferentially spaced about the fastening device, each lobeconstituting part of a semicircle, there being defined valleys betweenthe lobes. If D represents the distance between diametrically oppositeflats of one of the double hexagons defining the standard socket withina standard tolerance, G the radius of curvature of each lobe, F thediameter of the contour measured from the tips of diametrically oppositelobes, and B the diameter of the contour measured from diametricallyopposite valleys between the lobes, then the values of G, F, and B interms of the dimension D of the wrenching socket are given by theformulas set forth in FIGURE 5.

This application is a continuation-in-part of my copending applicationSer. No. 450,870 filed Apr. 26, 1965 and entitled Twelve-Lobe Fastener,now abandoned.

This invention relates generally to fastening devices and moreparticularly to a novel wrenching contour for a fastening device such asa bolt or nut.

Conventional bolts and nuts of the type used in military aircraft andmissiles must be torqued to high tensile preloads to resist reversalstress. Conventionally, these fasteners are provided with a twelve pointdouble hexagon wrenching contour for operation with standard wrenchingsockets, such as set forth in Federal Specification GGG-W-641. It isfound that in applying torque loads to these bolts or nuts, to unfastenthe same, the twelve point wrenching surfaces become eroded so that thejoint cannot be taken apart. In addition, hoop tension in the sockettool when it rotates about an eroded nut or bolt contour can crack thesocket.

The reason for the foregoing difiiculties is that in wrenching the boltor nut of conventional twelve point double hexagon contour with thestandard type of wrenchingv tool socket generally results in two orthree points of the recesses of the socket making contact with thepoints on the fastening contour rather than all twelve recesses andpoints respectively contacting each other. This relatively small numberof point contacts is a consequence of the double hexagon configurationof the socketsand fasteners and the tolerances permitted in themanufacture of the sockets and the fasteners themselves. In themechanical process of applying a high fastening or unfastenin'g torquewith the conventional standard socket and conventional contouredwrenching surface of the fastener, the load is so great at the two orthree contact points initially made that the points slide and are erodedso that the socket will skip around until perhaps two or three otherpoint contacts are made. These small number of contact points resultsagain in a large load on each contact point which again can cause theundesired erosion.

Patented Sept. 10, 1968 When all of the points are eroded, the slidingaction of the eroded points on the double hexagon shaped recesses of thesocket can so increase the hoop tension as to crack the socket itself.

While torque loads may be increased by providing specially designedwrenching contours for the wrenching tool socket and correspondingcontours for the'fastener such as a bolt or nut, there would be requiredthe provision of revised specifications for both fasteners and wrenchingsocket tools. As a practical matter, it therefore becomes desirable toprovide a modified wrenching contour for the fastener itself which willfit all standard wrenching sockets as presently set forth in FederalSpecifications.

With the foregoing considerations in mind, it is a primary object ofthis invention to provide a novel wrenching contour for a fastener whichwill enable a much higher torque to be applied for effecting a fastening or unfastening operation with a standard specified socket withoutthe risk of eroding the wrenching contour of the fastener of crackingthe socket itself all to the end that standard wrenching tools presentlyin use may be employed with the improved wrenching contour.

More particularly, it is an object to provide a novel wrenching contourfor a fastener for cooperation with a standard double hexagon typewrenching tool socket wherein twelve-point contact is effected as aconsequence of the wrenching contour configuration so that the torqueload is distributed at twelve points rather than only a few points withthe attendant advantage of a much higher torque capability beforefailure.

Still another object is to provide an improved wrenching contour for afastener wherein hoop tension created in the standard wrenching sockettool employed to apply torque to the fastener is considerably less for agiven torque than is the case with presently known wrenching surfaces.

Briefly, these and other objects and advantages of this invention areattained by providing a wrenching contour on a fastener for engagementby the recesses of a standard double hexagon wrenching tool socket ofmating size, the wrenching contour having twelve lobes each defined bypart of a semicircle and equally circumferentially spaced about thefastening device. The radius of curvature of each of the lobes inrelation to the diameter of the entire contour as measured from the tipsof diametrically opposite lobes and the diameter of the contour measuredfrom diametrically opposite valleys between the lobes are allinterrelated and dependent upon the size of the wrenching tool socket asmeasured between flats of one of the double hexagons defining thesocket. The relationships have been determined such as to effect atwelvepoint contact of the lobes by the recesses of the socket drivingtool after a certain torque has been applied to the end that the variousadvantages of decreased hoop tension and greater torqueing abilityresult.

A better understanding of the invention will be had by referring to oneembodiment thereof as illustrated in the accompanying drawings, inwhich:

FIGURE 1 is a perspective view illustrating a portion of a standarddriving t-ool socket for cooperation with a fastening device shownseparated from the socket having the novel wrenching contour of thisinvention;

FIGURE 2 is an end View of the fastening device taken in the directionof the arrows 22 of FIGURE 1;

FIGURE 3 is an end view of the standard socket taken in the direction ofthe arrows 3-3 of FIGURE 1;

FIGURE 4 is a grealy enlarged fragmentary view of a 0 portion of thewrenching contour of the fastener engaged 3 between various dimensionsdesignated in FIGURES 2, 3, and 4.

Referring first to FIGURE 1, there is shown a standard wrenching toolprovided with a socket 11 having recesses defined by a double hexagonconfiguration. This tool is normally employed for driving fasteners suchas bolts or nuts provided with a corresponding double hexagon wrenchingcontour surface. In such instances, as described heretofore, propertwelve-point contact is not always effected with the result of erosionof the points and consequent failure of the socket when given torquesare exceeded.

In accord with the present invention, a fastener such as a nut or boltillustrated at 12 in FIGURE 1 is provided with a novel wrenching contourdesignated generally by the numeral 13.

As seen best in FIGURE 2, the contour includes twelve lobes each definedin part by a semicircle and each being equally circumferentially spacedabout the fastener 12. This contour has a diameter as measured betweenthe tips of diameterically oposite lobes designated F. The diameter ofthe contour as measured between diametrically opposite valleys betweenthe lobes is indicated at B.

With reference now to the standard wrenching socket as shown in FIGURE3, the dimension or distance between opposite flats of one of the doublehexagons defining the recesses is designated D. This dimension isconventionally employed to designate the size of the wrenching tool.

FIGURE 4 illustrated the manner in which the socket engages thewrenching contour of the fastener. For example, the recessed flatportion 14a is defined by one fiat portion of one hexagon and theremaining portion of this fiat being designated 14b and connected to thefiat 14a by the dot-dashed line. The dimension D described in FIGURE 3may be used to designated the distance from this fiat to the center oraxis of the socket the dimension in FIGURE 4 being equal to D/2. Thecorresponding flats for the other of the two hexa'gons are shown at 15aand 15b in FIGURE 3.

The fiat 14a is shown engaging a specific lobe 16a in FIGURE 4 and thefiat 15a is shown engaging a lobe 16b. Lines drawn from the extremetrips of the lobes 16a and 16b to the center axis form an angle of 30 asindicated in FIGURE 4 for the twelve-lobe contour.

The radius of curvature of each of the lobes is of equal value and isdesignated G for the particular lobe 16b. This radius of curvature has avalue such that there are defined finite valleys between the lobes asindicated at 17a between the lobes 16a and 16b and 17b following r thelobe 16b and the next successive lobe. The radial distance of thesevalley from the central axis of the fastening device is designated B/2where B constitutes the diametric dimension between the valleys asdescribed in FIG- URE 2. In a similar manner, the radial distance of thetips of the lobes to the center of the device is shown at F/2 where F isas defined in FIGURE 2.

The values for G, F and B will be determined by the given dimension D ofthe particular wrenching socket employed. Thus, once a selected standardwrenching socket is provided, the configuration of the novel wrenchingcontour for the fastener is determined. In this respect, the variousrelationships for determining the correct values are given in the tableof FIGURE 5.

As shown in FIGURE 5, and as explained above, the dimension D is givenin that it is determined by the fiat to flat dimension of the standardsocket wrenching tool. The radius of curvature G for each of the lobesis then defined as having a minimum value of .08D where D is in inches.The maximum tolerance allowed in the provision of the radius ofcurvature dimension G is .004" and thus G may have values as indicatedin the table of FIGURE 5.

It should be understood that the dimension D itself will have valueswithin standard tolerances and thus there can exist a D minimumcondition and a D maximum condition which will also affect the value ofG.

The dimension F or tip or tip diametric measurement of the novelcontouring of this invention is then given by the formula illustrated inFIGURE 5, that is:

F=D-sec. 30-2G(sec. 30-1) the dimension B in turn is given by theformula as shown in FIGURE 5 B =g( 1+ sec. 15)

NQHL Dmin. mnt. min. mnx. min. mnx. min, mnx.

SIZE

l6".-. .316 .322 025 .029 .351 .354 .323 .327 384 030 O34 4Z1 424 387391 A 510 040 O44 564 567 518 522 G36 O50 054 712 716 647 653 For thespecific example of the one-half inch tool socket it was found that withthe old type of fastener contour constituting a double hexagonstructure, failure occurred under a torque of 2800 inch-pounds. With thesame stand ard one-half inch socket applied to the novel wrenchingcontour of the present invention, 4000 inch-pounds of torque wereapplied without any failure.

Referring once again to the enlarged fragmentary view of FIGURE 4, theactual operation taking place under wrenching torque will be described.With specific reference, for example, to the lobe 16b, it will be notedthat for a clockwise rotation of the socket, the lobe will bear againstthe recess flat 15a at the point 18. Because of the shape of the lobe asconstituting part of a semi-circle of a given radius of curvature G,this point or line engagement results in a slight brinelling rather thansliding action of the engaged surfaces. In other words, the circularshape permits a slight burying of the lobe into the recess so that allof the lobes will make contact as a consequence of this action after agiven torque has been applied. This action is contrary to that occurringin the event a standard double hexagon type contouring for the fastenerwere employed. In this latter instance, there would not be a point orline contact with the recess fiat 15a but rather a planar contact withthe result that should only two or three points engage, there would notbe the yelding necessary to effect twelve-point engagement. As aconsequence, the contacting portions of the conventional type of doublehexagon contour would have to bear the entire torque and the heretoforedescribed erosion will take place. In addition, a sliding action occurstending to bring the actual engagement away from the vertex point 19 andtowards the socket apex point 20.

The further away engagement of the recess flat 1511 from the apex 19occurs, the greater will be the stress as at the apex point 19 and it isat this point where cracking occurs in the conventional standard drivingsockets when driving conventional double hexagon fastener wrenchingcontours with too much torque.

When the lobe contour is employed as illustrated in FIGURE 4, there notonly results the advantage of twelve-point contact for the reasons setforth, but in addition, the contact points themselves such as at 18 areconsiderably closer to the apex 19 and thus the reaction forces do notresult in as great a stress at the point 19. Further, because of thetwelve-point contact, the actual forces involved at each point ofcontact are considerably less than is the case when only a few pointsare contacted as characterizes the situation with prior art fastenerstorqued with standard sockets as described.

The radius of curvature of the lobes designated G is fairly critical asindicated by the table in FIGURE 5. If the radius of curvature is toolarge, the desirable feature of line point contact when viewed as inFIGURE 4 is lost and the engagement of all twelve points will not takeplace until a considerably higher torque is applied. On the other hand,if the radius is too small, there cannot be provided a contact pointsufliciently close to the apex 19 to avoid undue stressing at this apexpoint. The optimum value of this radius of curvature is indicated inFIGURE 4 wherein if a normal is drawn to the contact point 18, itcoincides with the radius of curvature and forms an angle of 30 withrespect to the horizontal line passing from the center through the apex19.

From the foregoing description, it will thus be evident that the presentinvention has provided a novel wrenching contour for a fastening devicewherein the various objects set forth heretofore are fully realized.

What is claimed is:

1. A fastening device having a wrenching contour for engagement by therecesses of a standard double hexagon wrenching tool socket of matingsize D, where D is the distance between diametrically opposite flats ofone of the double hexagons defining said socket within a standardtolerance, said wrenching contour having twelve lobes each defined bypart of a semicircle, and each equally circumferentially spaced aboutsaid device, and in which, if G is the radius of curvature of each ofsaid lobes, F the diameter of said contour measured from the tips ofdiametrically opposite lobes, and B the diameter of said contourmeasured from diametrically opposite valleys between the lobes, then G,F, and B are defined as follows:

where D is given in inches;

F=D-sec. 302G(sec. 30l) and References Cited UNITED STATES PATENTS2,083,092 6/1937 Richer 8545 2,895,368 7/1959 Place 85-9 2,969,2501/1961 Kull 8545 3,140,636 7/1964 Grimm 85-32 3,290,982 12/1966Marschner 851 FOREIGN PATENTS 1,273,228 8/1961 France.

CARL W. TOMLIN, Primary Examiner.

RAMON S. BRITTS, Assistant Examiner.

